"""SAP 10.2 Table 12a — high-rate fractions for off-peak tariffs.

Sourced verbatim from `domain/sap10_calculator/docs/specs/sap-10-2-full-specification-2025-
03-14.pdf`, page 191 (Table 12a). RdSAP10 §19.1 cross-references this
table from RdSAP10 §10a/§10b — the table is not duplicated in the
RdSAP10 PDF.

Two grids:
- Grid 1: space + water heating systems × tariff → (SH_frac, WH_frac)
- Grid 2: other electricity uses × tariff → fraction

For STANDARD tariff (no off-peak split) every lookup returns 1.0 —
all consumption at the unit price.
"""

from __future__ import annotations

from enum import Enum
from typing import Final, Optional


class Table12aSystem(Enum):
    """Table 12a row label (System column) for the space + water heating
    fractions grid. Each member maps to a row of PDF page 191. Three
    rows that require external sources (Electric CPSU → Appendix F;
    Immersion / HP-DHW-only → Table 13) are reachable via lookup but
    raise `NotImplementedError` until a fixture exercises them."""

    INTEGRATED_STORAGE_DIRECT = "integrated_storage_direct"
    OTHER_STORAGE_HEATERS = "other_storage_heaters"
    ELECTRIC_DRY_CORE_OR_WATER_STORAGE = "electric_dry_core_or_water_storage"
    DIRECT_ACTING_ELECTRIC_BOILER = "direct_acting_electric_boiler"
    ELECTRIC_CPSU = "electric_cpsu"
    UNDERFLOOR_HEATING = "underfloor_heating"
    GSHP_APP_N = "gshp_app_n"
    GSHP_OTHER = "gshp_other"
    GSHP_OTHER_OFF_PEAK_IMMERSION = "gshp_other_off_peak_immersion"
    GSHP_OTHER_NO_IMMERSION = "gshp_other_no_immersion"
    ASHP_APP_N = "ashp_app_n"
    ASHP_OTHER = "ashp_other"
    ASHP_OTHER_OFF_PEAK_IMMERSION = "ashp_other_off_peak_immersion"
    ASHP_OTHER_NO_IMMERSION = "ashp_other_no_immersion"
    OTHER_DIRECT_ACTING_ELECTRIC = "other_direct_acting_electric"
    IMMERSION_OR_HP_DHW_ONLY = "immersion_or_hp_dhw_only"


class OtherUse(Enum):
    """Table 12a Grid 2 row label — "Other electricity uses" sub-table.
    Maps end-uses (pumps/fans/lighting/PV-credit) to their off-peak
    high-rate fraction. Pumps + lighting + locally-generated electricity
    use ALL_OTHER_USES; mechanical-ventilation fans use the dedicated
    FANS_FOR_MECH_VENT row."""

    FANS_FOR_MECH_VENT = "fans_for_mech_vent"
    ALL_OTHER_USES = "all_other_uses"


class Tariff(Enum):
    """Electricity tariff column in Table 12a. TEN_HOUR is in the spec
    but unreachable from RdSAP10 cert flow (meter_type enum 1..5 has no
    10-hour code) — kept for worksheet-shape fidelity."""

    STANDARD = "standard"
    SEVEN_HOUR = "7-hour"
    TEN_HOUR = "10-hour"
    EIGHTEEN_HOUR = "18-hour"
    TWENTY_FOUR_HOUR = "24-hour"


# RdSAP cert `meter_type` integer enum → Table 12a tariff column.
# String forms accepted by lower-casing + stripping.
_METER_INT_TO_TARIFF: Final[dict[int, Tariff]] = {
    1: Tariff.SEVEN_HOUR,         # Dual
    2: Tariff.STANDARD,           # Single
    3: Tariff.STANDARD,           # Unknown (per Q11b — spec-faithful)
    4: Tariff.TWENTY_FOUR_HOUR,   # Dual (24 hour)
    5: Tariff.EIGHTEEN_HOUR,      # Off-peak 18 hour
}

_METER_STR_TO_INT: Final[dict[str, int]] = {
    "single": 2,
    "standard": 2,
    "dual": 1,
    "dual (24 hour)": 4,
    "off-peak 18 hour": 5,
    # RdSAP 10 §17 page 85 row 10-2 lodging form: "18-hour" (Elmhurst
    # Summary §14.2 surfaces this as the bare "18 Hour"). Per §12
    # page 62: "if the meter is dual 18-hour/24-hour it is 18-hour/
    # 24-hour tariff" → enum 5 (EIGHTEEN_HOUR).
    "18 hour": 5,
    "unknown": 3,
    "": 3,
}


# Table 12a Grid 1 SH column — high-rate fraction by (system, tariff).
# Only spec-listed (system, tariff) pairs appear; combos not in the
# table raise NotImplementedError at lookup time. Sourced verbatim from
# SAP10.2 PDF page 191.
_SH_HIGH_RATE_FRACTION: Final[dict[tuple[Table12aSystem, Tariff], float]] = {
    (Table12aSystem.INTEGRATED_STORAGE_DIRECT, Tariff.SEVEN_HOUR): 0.20,
    (Table12aSystem.OTHER_STORAGE_HEATERS, Tariff.SEVEN_HOUR): 0.00,
    (Table12aSystem.OTHER_STORAGE_HEATERS, Tariff.TWENTY_FOUR_HOUR): 0.00,
    (Table12aSystem.ELECTRIC_DRY_CORE_OR_WATER_STORAGE, Tariff.SEVEN_HOUR): 0.00,
    (Table12aSystem.DIRECT_ACTING_ELECTRIC_BOILER, Tariff.SEVEN_HOUR): 0.90,
    (Table12aSystem.DIRECT_ACTING_ELECTRIC_BOILER, Tariff.TEN_HOUR): 0.50,
    (Table12aSystem.UNDERFLOOR_HEATING, Tariff.SEVEN_HOUR): 0.90,
    (Table12aSystem.UNDERFLOOR_HEATING, Tariff.TEN_HOUR): 0.50,
    (Table12aSystem.GSHP_APP_N, Tariff.SEVEN_HOUR): 0.80,
    (Table12aSystem.GSHP_APP_N, Tariff.TEN_HOUR): 0.80,
    (Table12aSystem.GSHP_OTHER, Tariff.SEVEN_HOUR): 0.70,
    (Table12aSystem.GSHP_OTHER, Tariff.TEN_HOUR): 0.60,
    (Table12aSystem.ASHP_APP_N, Tariff.SEVEN_HOUR): 0.80,
    (Table12aSystem.ASHP_APP_N, Tariff.TEN_HOUR): 0.80,
    (Table12aSystem.ASHP_OTHER, Tariff.SEVEN_HOUR): 0.90,
    (Table12aSystem.ASHP_OTHER, Tariff.TEN_HOUR): 0.60,
    (Table12aSystem.OTHER_DIRECT_ACTING_ELECTRIC, Tariff.SEVEN_HOUR): 1.00,
    (Table12aSystem.OTHER_DIRECT_ACTING_ELECTRIC, Tariff.TEN_HOUR): 0.50,
}


# Table 12a Grid 1 WH column. Only heat-pump WH rows carry off-peak
# fractions in scope A; Electric CPSU (Appendix F) and immersion /
# HP-DHW (Table 13) raise on lookup until those slices land.
_WH_HIGH_RATE_FRACTION: Final[dict[tuple[Table12aSystem, Tariff], float]] = {
    (Table12aSystem.GSHP_APP_N, Tariff.SEVEN_HOUR): 0.70,
    (Table12aSystem.GSHP_APP_N, Tariff.TEN_HOUR): 0.70,
    (Table12aSystem.GSHP_OTHER_OFF_PEAK_IMMERSION, Tariff.SEVEN_HOUR): 0.17,
    (Table12aSystem.GSHP_OTHER_OFF_PEAK_IMMERSION, Tariff.TEN_HOUR): 0.17,
    (Table12aSystem.GSHP_OTHER_NO_IMMERSION, Tariff.SEVEN_HOUR): 0.70,
    (Table12aSystem.GSHP_OTHER_NO_IMMERSION, Tariff.TEN_HOUR): 0.70,
    (Table12aSystem.ASHP_APP_N, Tariff.SEVEN_HOUR): 0.70,
    (Table12aSystem.ASHP_APP_N, Tariff.TEN_HOUR): 0.70,
    (Table12aSystem.ASHP_OTHER_OFF_PEAK_IMMERSION, Tariff.SEVEN_HOUR): 0.17,
    (Table12aSystem.ASHP_OTHER_OFF_PEAK_IMMERSION, Tariff.TEN_HOUR): 0.17,
    (Table12aSystem.ASHP_OTHER_NO_IMMERSION, Tariff.SEVEN_HOUR): 0.70,
    (Table12aSystem.ASHP_OTHER_NO_IMMERSION, Tariff.TEN_HOUR): 0.70,
}


def water_heating_high_rate_fraction(
    system: Table12aSystem, tariff: Tariff
) -> float:
    """Table 12a Grid 1 WH column lookup. Returns the fraction of water-
    heating consumption billed at the high rate. STANDARD tariff → 1.0
    (passthrough). Heat-pump WH rows return spec fractions. Immersion /
    HP-DHW-only (Table 13) and Electric CPSU (Appendix F) raise."""
    if tariff is Tariff.STANDARD:
        return 1.0
    fraction = _WH_HIGH_RATE_FRACTION.get((system, tariff))
    if fraction is None:
        raise NotImplementedError((system, tariff))
    return fraction


def space_heating_high_rate_fraction(
    system: Table12aSystem, tariff: Tariff
) -> float:
    """Table 12a Grid 1 SH column lookup. Returns the fraction of space-
    heating consumption billed at the high rate. STANDARD tariff has no
    off-peak split, so every system returns 1.0 (passthrough). Spec-
    listed off-peak (system, tariff) pairs return the published
    fraction; unlisted pairs (incl. Electric CPSU → Appendix F and
    immersion / HP-DHW → Table 13) raise."""
    if tariff is Tariff.STANDARD:
        return 1.0
    fraction = _SH_HIGH_RATE_FRACTION.get((system, tariff))
    if fraction is None:
        raise NotImplementedError((system, tariff))
    return fraction


# Table 12a Grid 2 — "Other electricity uses" sub-table.
_OTHER_USE_HIGH_RATE_FRACTION: Final[dict[tuple[OtherUse, Tariff], float]] = {
    (OtherUse.FANS_FOR_MECH_VENT, Tariff.SEVEN_HOUR): 0.71,
    (OtherUse.FANS_FOR_MECH_VENT, Tariff.TEN_HOUR): 0.58,
    (OtherUse.ALL_OTHER_USES, Tariff.SEVEN_HOUR): 0.90,
    (OtherUse.ALL_OTHER_USES, Tariff.TEN_HOUR): 0.80,
}


def other_use_high_rate_fraction(use: OtherUse, tariff: Tariff) -> float:
    """Table 12a Grid 2 lookup — fraction of an "other electricity use"
    consumption billed at the high rate. STANDARD → 1.0. 18-hour /
    24-hour tariffs aren't in Grid 2; the spec implicitly applies the
    same logic via Grid 1 for those tariffs, so this lookup raises for
    them."""
    if tariff is Tariff.STANDARD:
        return 1.0
    fraction = _OTHER_USE_HIGH_RATE_FRACTION.get((use, tariff))
    if fraction is None:
        raise NotImplementedError((use, tariff))
    return fraction


def tariff_from_meter_type(meter_type: object) -> Tariff:
    """Resolve the RdSAP cert `meter_type` field to a Table 12a tariff
    column. Absent (None / "") → STANDARD (no off-peak split applied)
    per the Q11b spec-faithful policy.

    Strict-dispatch per [[reference-unmapped-sap-code]]: lodging present
    but unmapped (integer outside enum 1..5, or string not in the
    accepted set) raises `UnmappedSapCode`. Empty string maps to
    "unknown" code 3 → STANDARD (the explicit absent-sentinel).

    NOTE: for a Dual meter the §12 dispatch (Rules 1-4 page 62)
    requires the main heating SAP codes to choose between 7-hour and
    10-hour. This helper returns the SEVEN_HOUR default for Dual —
    callers that have access to the main heating codes should use
    `rdsap_tariff_for_cert` instead.
    """
    from domain.sap10_calculator.exceptions import UnmappedSapCode

    if meter_type is None:
        return Tariff.STANDARD
    if isinstance(meter_type, int):
        if meter_type in _METER_INT_TO_TARIFF:
            return _METER_INT_TO_TARIFF[meter_type]
        raise UnmappedSapCode("meter_type", meter_type)
    if isinstance(meter_type, str):
        key = meter_type.strip().lower()
        # Digit-string forms (e.g. '2') route via int-cast first; the
        # str dict only carries the enum word aliases ('single', 'dual',
        # 'unknown', ...). The empty-string alias maps to "unknown"
        # (code 3) per the dict — that's the explicit absent sentinel.
        if key in _METER_STR_TO_INT:
            return _METER_INT_TO_TARIFF[_METER_STR_TO_INT[key]]
        if key.isdigit():
            digit_code = int(key)
            if digit_code in _METER_INT_TO_TARIFF:
                return _METER_INT_TO_TARIFF[digit_code]
            raise UnmappedSapCode("meter_type", meter_type)
        raise UnmappedSapCode("meter_type", meter_type)
    raise UnmappedSapCode("meter_type", meter_type)


# RdSAP 10 §12 page 62 — SAP main heating code sets for the Dual-meter
# tariff dispatch. Each rule's set is taken verbatim from §12 Rules 1-3.
# Rule 1: Electric CPSU → 10-hour
_RULE_1_CPSU_CODES: Final[frozenset[int]] = frozenset({192})
# Rule 2: storage-based electric → 7-hour. The (421, 422) underfloor
# subset is explicit per §12 ("421 or 422, but not 424") — 423 / 425
# fall through to Rule 4 default unless a later spec amendment adds
# them.
_RULE_2_STORAGE_CODES: Final[frozenset[int]] = frozenset(
    list(range(401, 410))   # electric storage heaters 401-409
    + [193, 195]            # electric dry-core / water-storage boiler
    + [421, 422]            # electric underfloor heating (424 excluded)
)
# Rule 3: direct-acting electric + heat pumps + electric room heaters
# → 10-hour. §12 lists "heat pump (211 to 224, 521 to 524, or
# database)" — the "database" branch fires when the cert lodges a
# PCDB Table 362 heat-pump index regardless of SAP code.
_RULE_3_TEN_HOUR_CODES: Final[frozenset[int]] = frozenset(
    [191]                       # direct-acting electric boiler
    + list(range(211, 225))     # heat pumps 211-224
    + list(range(521, 525))     # warm-air heat pumps 521-524
    # TODO: electric room heater codes (SAP Table 4a row 6xx for
    # electric panel / radiant heaters) when a fixture surfaces them.
)


def rdsap_tariff_for_cert(
    meter_type: object,
    *,
    main_1_sap_code: Optional[int] = None,
    main_2_sap_code: Optional[int] = None,
    main_1_is_heat_pump_database: bool = False,
    main_2_is_heat_pump_database: bool = False,
) -> Tariff:
    """RdSAP 10 §12 page 62 — full meter+heating tariff dispatch.

    Single meter → STANDARD. Dual 18-hour / Dual 24-hour map straight
    to their respective tariffs. Otherwise applies §12 Rules 1-4
    where each rule considers BOTH main heating systems on multi-
    main certs ("the main system or either main system if there are
    two"):

      Rule 1  Electric CPSU (192)                    → 10-hour
      Rule 2  Storage / storage boiler / underfloor  → 7-hour
              (401-409, 193, 195, 421, 422)
      Rule 3  Direct-acting electric boiler (191),   → 10-hour
              heat pump (211-224, 521-524, database),
              electric room heaters
      Rule 4  None of the above                      → 7-hour
              (default for Dual + non-electric main)

    `main_1_is_heat_pump_database` / `main_2_is_heat_pump_database`
    signal the "or database" Rule 3 branch — the cert lodges a PCDB
    Table 362 heat-pump record. Callers compute this via
    `heat_pump_record(main_heating_index_number) is not None`.

    Cert 000565 (Main 1 SAP code 224 ASHP + Dual meter) → Rule 3 →
    TEN_HOUR, matching the worksheet's "10 Hour Off Peak" lodging.
    """
    base = tariff_from_meter_type(meter_type)
    # Non-Dual meters resolve straight from the meter type.
    if base is not Tariff.SEVEN_HOUR:
        return base
    main_codes = {
        c for c in (main_1_sap_code, main_2_sap_code) if c is not None
    }
    # Rule 1
    if main_codes & _RULE_1_CPSU_CODES:
        return Tariff.TEN_HOUR
    # Rule 2 — checked BEFORE rule 3 per §12 ordering (storage takes
    # precedence over the broader Rule 3 electric set).
    if main_codes & _RULE_2_STORAGE_CODES:
        return Tariff.SEVEN_HOUR
    # Rule 3
    if main_codes & _RULE_3_TEN_HOUR_CODES:
        return Tariff.TEN_HOUR
    if main_1_is_heat_pump_database or main_2_is_heat_pump_database:
        return Tariff.TEN_HOUR
    # Rule 4 — default
    return Tariff.SEVEN_HOUR